ANALOGY OF FINS TO WINGS. 39 



tunnies, of which the bonitos and albicores of seamen 

 are only different species, will sometimes, in a stiff gale, 

 play about a vessel in full sail, with as much ease as if 

 she was perfectly still — one moment they will be near 

 the stern, while the next, as if by a single dart, they are 

 many yards ahead of the bowsprit : this we have re- 

 peatedly witnessed; and the thought then struck us that 

 no fish, by any possibility, could move more rapidly. In 

 comparing, therefore, the functions of the pectoral and 

 caudal fins of fishes to the wings and tails of birds, we 

 find they are perfectly analogous, and that their import- 

 ance, as furnishing generic characters, is equally great. 



(40.) It is somewhat remarkable, that although many 

 instances occur among swift-flying birds where the 

 wings are pointed and the tail rounded, yet in the class 

 of fishes, the shape of the pectoral and the caudal fins are 

 almost always symmetrical ; that is to say, the caudal is 

 forked in the same proportion as the pectorals are 

 pointed; nor does an instance at this moment occur to 

 us where the pectoral is pointed and the caudal rounded, 

 or the contrary : hence we may infer that the caudal 

 fin in fishes is more important in its offices than is the 

 tail in birds, and this is an additional argument in 

 favour of the importance we attach to this member. 



(41.) A comprehensive view of the coincidences in 

 the formation of the dorsal and ventral fins in genera 

 widely distinct in affinity from each other, will lead 

 the philosophic naturalist to suspect that these may 

 offer one of the best clues for determining the ana- 

 logical relations of widely separated groups. This 

 intricate subject has claimed much of our attention ; 

 and although, from its nature, we have been obliged to 

 leave it unfinished, the progress we have made seems 

 to sanction the following observations : — It would ap- 

 pear that in every one of the tribes composing the two 

 orders of osseous fishes (the Acanthopteryges and the 

 Malacopteryges), the two chief divisions are characterised, 

 the one by having the dorsal fin single, while in the 

 latter it is double, or at least deeply cleft : in another 



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